Carrier transmission system



July 7, 1942.

N. BOTSFORD 2,289,174

CARRIER TRANSMISSION SYSTEM Filed Dec. 4, 1940 f5 7 50 EMERGY NORMAL M00 M00 NORMAL CARR/ER souecs lbo /o $64 EMEncr I CARR/ER SOUR" EMERGY NORMAL SOURCE sMe/aar osmn omoo lNVENTOR y N. TSFORD A TTORNEV Patented July 7,

CARRIER TRANSMISSION SYSTEM Nelson Botsford, Rutherford, N. J.',- asslgnor to ,Bell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application December 4, 1940, Serial No. 368,415

11 Claims. (01. 178-44) This invention relates to a carrier wave transmission system, and moreparticularly to a magnetic core coil arrangement for efiectively connecting in such system normal and emergency carrier apparatus comprising modulators, de-

modulators and carrier wave generators.

In certain carrier transmission systems it may be desirable to provide both normal and emergency apparatus including modulators, demodulators and carrier wave generators so as to maintain continuity of transmission regardless of the occurrence of a fault on either the normal or emergency apparatus. Such provision ordinarily requires a multiplicity of magnetic core coils to connect operatively the various normal and emergency apparatus in the system. In designing a carrier system of this type, the nun ber of such coils is a principal consideration, especially from the viewpoints of cost, modulation efiect, tolerable over-all transmission loss, impedance matching and reflection requirements.

Accordingly, the present invention contemplates a magnetic core coil arrangement to connect electromagnetically the normal and emergency carrier generators to the normal and emergency modulators and demodulators in a carrier wave transmission system in such manner as to require substantially a minimum number of magnetic core coils while at the same time to isolate electrically each modulator or demodulator from the other modulators and demodulators and the normal and emergency carrier generators from each other.

It is an object of the invention to supply carrier waves simultaneously to both normal and emergency modulating and demodulating apparatus.

It is another object to render selectively eifective the normal and emergency carrier apparatus in incoming and outgoing transmission paths.

It is a further object to preclude electrical interference between the idle and operative carrier apparatus.

It is still another object to obviate electrical interference between the normal and emergency carrier generators.

It is a still further object to minimize the effects of faults in the normal and emergency carrier apparatus.

It is also an object to isolate electrically each modulator or demodulator from the other modulators and demodulators.

Carrier transmission systems of a conventional type embody a signal source, an outgoing line, an

mal and emergency apparatus including modulators, demodulators and carrier wave generators, and suitable switching devices to render efiective selectively the modulators, demodulators and carrier wave generators in the respective outgoing and incoming lines.

In a preferred embodiment, the present invention comprises a plurality of multiwinding magnetic core coils for connecting electromagnetically the normal and emergency apparatus such that relatively low transmission loss is efiectively provided between the carrier generators and both the modulators and demodulators, and relatively high transmission loss is eflectively provided between the normal and emergency carrier generators, between the normal modulator and demodulator, between the emergency modulator and demodulator and between each modulator or demodulator and the other modulators and demodulators. Accordingly, carrier wave energy may be supplied from either of the carrier generators to the normal and emergency modulators and demodulators simultaneously, and each modulator or demodulator is isolated electrically from the other modulators and demodulators. This isolation renders it possible to apply the normal and emergency modulators and demodulators interchangeably to the outgoing and incoming lines.

The invention will be readily understood from the following description taken together with the accompanying drawing. in which:

Figs. 1 and 2 illustrate the invention in its simplest forms to connect electromagnetically two circuits having a high transmission loss therebetween with two other circuits having a high transmission loss therebetween; and

Figs. 3 and 4 represent the respective arrangements of Figs. 1 and 2'embodied in carrier transmission systems.

The same reference numerals are utilized to designate identical elements appearing in the several figures of the drawing.

Fig. 1 illustrates an electromagnetic coupling of circuits A and B with circuits C and .D, and comprises branch Ill including the circuits A and B, equal windings II and' I2 and a balancing network I3 applied across the junctions of the windings I I and I2 and of one side of the circuits A and B, and branch it including the circuits C and D, equal windings I5 and I6 and a balancing network l'l connected to the Junctions of the windings I5 and I6 and of one side of the circuits C and D. The circuits A, B, C and D are electroincoming line, signal translating apparatus, nor- 55 magnetically coupled by having the windings ll,

II, II and I8 wound on a common magnetic core l8. Shield I8 is applied to ground connection 28.

Transmission following the well-known action of hybrid coils is effected among the several circuits of Fig. 1 as follows:

Circuit A to circuits C and D and network I! CircuitB to circuits C and D and network II Circuit C to circuits A and B and network l1 Circuit D in circuits A and B and network I1 High attenuation among the several circuits of Fig, 1 is provided as follows:

Circuit A and 18 Circuit A and network l1 Circuit B and network l1 Circuit C and circuit D Circuit C and network I 8 Circuit D and network l8 Network l8 and network l1 Fig. 2 shows an electromagnetic connection of circuits E and F with circuits G and H. and comprises circuit E connected to equal windings 28 and 28, circuit 1'' connected to equal windings 21 and 28, circuit G connected to equal windings 28 and 80, and circuit H connected to equal windings 8| and 82. The circuits E, F, G and H are electromagnetically connected by applying windings 2! and 21 to magnetic core 88, windings 28 and 28 and windings 28 and 2| to magnetic core 84, and windings 80 and 82 to magnetic core 85. Winding 81 coupling balancing network 88 to the windings and 21 is associated with both latter windings on the magnetic core 88, and winding 88 coupling balancing network 88 to the windings 80 and 82 is associated with both latter windings on the magnetic core 85.

windings 21 and 28 are connected in seriesaiding relationship and windings 28 and 28 are connected in a series-opposing relationship which relationships are such that, assuming an observonce of the requirements concerning the relations between terminations and the winding ratios, core reluctance and other design characteristics, a voltage applied across the windings 21 and 28 serves to induce equal and opposing voltages in the windings 25 and 28. Similarly, a voltage applied across the windings 25 and 28 serves to effect equal and opposite voltages in the windings 21 and 28. Likewise identical situations obtain with regard to the series-aiding windings 8| and 82 and the series-opposing windings 28 and Ill. Consequently, substantially no transmission takes place between the circuits E and F, and between the circuits G and H.

Transmission among the several circuits of Fig. 2 is provided as follows: a

Circuit E to circuits G and H and network 88 Circuit F to circuits G and H and network 86 Circuit G to circuits E and F and network 88 Circuit H to circuits E and F and network 88 High attenuation among the several circuits of Fig. 2 is effected as follows:

Circuit E and circuit 1'' Circuit E and network 88 Circuit 1'' and network 88 Circuit G and circuit H Circuit G and network 88 Circuit H and network 88 Network 88 and network 88 Fig. 3 shows a modification of a combination of the arrangements of Figs. 1 and 2 embodied in a carrier transmission system in which a normal modulator 80 has its respective input and output connected to a signal source SI and an outgoing transmission line 82 via the closed coniacts of normally unoperated electromagnetic respear-:4

lay 80, and a normal demodulator 88 has its respective input and output applied to an incoming transmission line 54 and suitable signal translating apparatus 58 through the closed contacts of normally unoperated electromagnetic relay 8|. Branch 49 supplying normal or emergency carrier waves to the modulator and demodulators 52 in a manner to be explained subsequently embodies in one common side the equal windings I5 and it across whose junction and another common side of the branch 49 is applied the balancing network l1. a

An emergency modulator 51 has its respective input and output connected to the signal source ii and outgoing transmission line 52 via the open contacts of the normally unoperated electromagnetic relay 60, and an emergency demodulator 58 has its respective input and output connected to the incoming transmission line 54 and translating apparatus 88 through the open contacts of the normally unoperated electromagnetic relay 6|. Branch 48 supplying normal or emergency carrier waves to the emergency modulator 51 and emergency demodulator 58, in a manner to be explained hereinafter, includes in one common side the equal windings H and I2 across whose junction and another common side of the branch 48 is applied the balancing network II.

A normal carrier generator 86 is connected through a pair of closed contacts 45, 45 of normally unoperated electromagnetic relay 48 to the equal and series-opposing windings 25 and 28, and an emergency carrier generator 59 is connected through a pair of open contacts 41, 41 of the normally unoperated relay 48 to the equal and series-aiding windings 21 and 28. Thus, the respective normal and emergency carrier sources 56 and 58 may be individually applied to their associated windings 25 and 28, and 21 and 28 under control of the relay 46 in a manner and for a purpose, both of which will be hereinafter explained. It is to be understood that the modulators and demodulators may be of any well-known type. Windings ll, I2, 25 and 21 are wound on a magnetic core 65, and windings l5, I8, 28 and 28 are wound on a magnetic core 88. The shields IQ of both cores may be appliedto the ground connection 28.

In the normal operation of Fig. 3, carrier voltage of the normal carrier source 58 is simultaneously transmitted via the closed contacts 45, 45 of the relay 46 to both the normal and emergency carrier branches 48 and 49 by the electromagnetic connection of the windings 25 and 28 with the windings H, l2, l5 and it. Therefore, the normal carrier voltage is simultaneously available in the normal modulator and demodulator and in the emergency modulator and demodulator with substantially no transmission loss. As previously pointed out, the respective normal modulator and demodulator and emergency modulator and demodulator are connected through the closed and open contacts of the normally unoperated relays 68 and 8| to the signal source and outgoing line and to the signal translating apparatus and incoming line. Consequently, the normal carrier voltage is effective in the normal modulator and demodulator and ineiiective in the emergency modulator and demodulator in so far as any effect on signals in the respective outgoing and incoming transmission lines 52 and 54 is concerned.

A voltage applied at either the normal modulator orv the normal demodulator would cause approximately equal currents to flow in the respective normal and emergency. carrier branches 61 and 68 for the reason that the impedances of the carrier sources 56 and 59 are relatively high as compared with those of respective equal resistances 63 and 64 applied thereacross. These equal currents cause substantially equal and opposite flux in the core 65. Accordingly, relatively high transmission loss would exist from either the normal modulator or the normal demodulator to both the emergency modulator and demodulator so that substantially no transmission would occur from either of the former to the latter. In addition, the hybrid action of the respective pairs of windings II and I2 and I5 and I6 causes a relatively high transmission loss to exist between the normal modulator and normal demodulator, and between the emergency modulator and emergency demodulator.

Due to the previously mentioned effect of the series-opposing and series-aiding relationship of the respective windings 25 and 26, and 21 and 28, a voltage from the normal carrier source 56 would cause equal and opposite voltages to be induced in the windings 21 and 28. Hence, the normal carrier voltage would cause substantially no normal carrier current to flow in the emergency carrier circuit 68. Therefore, relatively high transmission loss would exist from the normal carrier branch 61 to the emergency carrier branch 68.

Assuming the occurrence of a failure of the normal carrier source 56 of Fig. 3, then the relay 46 is energized from battery 15 by manually closing switch 16. This operates the relay 46 to open the pair of contacts 45, 45 and to close the pair of contacts 41, 41. Now, the emergency carrier generator is applied to its associated windings 21 and 28, and the normal carrier source is disconnected from its associated windings 25 and 26. Therefore, the emergency carrier voltage is simultaneously available to the emergency modulator and demodulator and to the normal modulator and demodulator with substantially no transmission loss.

Assuming further that faults occur in the normal modulator and in the normal demodulator, the switches 16 and 11 are closed to energize the relays 60 and 6| from the batteries 18 and 19, respectively. These relays operate to close their contacts associated with the emergency modulator and demodulator and to open their contacts associated with the normal modulator and demodulator. Accordingly, the emergency carrier voltage is eil'ective in the emergency modulator and demodulator and ineffective in the normal modulator and demodulator, in so far as any efiect on signals in the respective outgoing and incoming transmission lines 52 and 54 is concerned.

Due to the previously pointed out effect of the series-opposing and series-aiding relationship of the respective windings 25 and 26, and 21 and 28, a voltage from the emergency carrier source 59 would cause equal and opposite voltages to beinduced in the windings 25 and 26. Consequently, the emergency carrier voltage would cause substantially no emergency carrier current to flow in the normal carrier circuit 61. Hence, relatively high transmission loss would exist from the emergency carrier branch 68 to the normal carrierbranch 61.

A voltage applied at either the emergency modulator or demodulator in Fig. 3 would cause approximately equal currents to flow in the resistances 63 and 64 of the respective normal and emergency carrier branches 61 and 68. because of the impedance diflerence between the carrier sources 56 and 59 and the resistances 63 and 64 Y and therefore would cause the production or gency modulator and demodulator for the reasons mentioned above in connection therewith with respect to the normal operation of Fig. 3.

Fig, 4 is an alternate form of the invention, and comprises the arrangement of Fig. 2 embodied in the carrier transmission system described and illustrated above in connection with Fig. 3. It will be noted that the system of Fig. 4 includes four wound magnetic cores which number is double that required in Fig. 3. The arrangement of Fig. 4 permits greater isolation between the normal and emergency carrier apparatus, utilizes no metallic connections between any oi. the several circuits, and allows considerable flexibility in the selection of balancing network impedances as the latter are associated with their individual windings as it will be presently seen.

, Referring to Fig. 4, the normal modulator and demodulator are connected to respective pairs of equal windings 90 and 9I, and 92 and 93; the normal and emergency carrier sources are connected to respective pairs of equal windings 94 and 95, and 96 and 91; and the emergency modulator and demodulator are connected to respective pairs of equal windings 98 and 99, and I 00 and IN. Coupled with the windings 9I and 93 is a winding I02 applied to the balancing network 38, and coupled withthe windings 96 and I00 is winding I04 applied to the balancing network 36. Windings 9|, 93 and I02 are wound on magnetic core I06; windings 90, 92, 95 and 91 are wound on magnetic core I01; windings 94, 96, 99 and IN are wound on magnetic core I08; and windings 98, I00 and I04 are wound on magnetic core I09. Discrete pairs of windings 90 and 9I, 94 and 95, and 98 and 99 are each connected in series-opposing relationship, and the discrete pairs of windings 92 and 93, and 96 and 91, and I00 and IN are each connected in seriesaiding relationship.

In the normal operation of Fig. 4, a'carrier voltage from the normal carrier source is simultaneously available to the normal modulator and demodulator as well as to the emergency modulator and demodulator, although it is effective I only in the normal modulator and demodulator,

the former to the latter. In addition, the action hereinbefore described in connection with Fig. 2

between the series-opposing windings and 9| and the series-aiding windings 92 and 93 causes a high loss between the normal modulator and demodulator. Similarly, the action between the series-opposing windings II and II and the seriesthe series-opposing and series-aiding relationship of the windings l4 and II, and N and 91, a voltage from the normal carrier source I would cause equal and opposite voltages to be induced in the latter windings. Therefore, the normal carrier voltage would cause substantially no normal carrier current to flow in the emergency carrier circuit is. Hence, relatively high transmission loss exists from the carrier branches .1 to the carrier branch 68. Thus, the foregoing action of Fig. 4 is substantially identical with the corresponding action of Fig. 3.

In the event of a failure oi the normal carrier source 56 of Fig. 4, the relay 4' is energized to apply the emergency carrier source 59 to its associated windings 98 and ll, and at the same time to disconnect the normal carrier source 56 from its associated windings l4 and 95. Now

Obviously, a manipulation of the relays 4t, 60 and II may enable either the normal or emergency carrier sources to be associated operatively with any desired combination of the normal and emergency modulators and demodulators, in so far as a connection to the coil windings is concerned without impairing the effectiveness of the signaling system; the idle or out-of-service apparatus may be tested without interfering with signaling transmission on the outgoing and incoming lines; and, although not shown, the individual modulators and demodulators may be interchangeably applied in any desired combination {:1 both the outgoing and incoming transmission An electromagnetic connection of the normal and emergency apparatus in a carrier transmisthe emergency carrier voltage is simultaneously available in the emergency modulator and demodulator and in the normal modulator and demodulator with substantially no transmission loss. Assuming further the occurrence of faults in the normal modulator and demodulator, the relays 60 and ii are operated to close their contacts associated with the emergency modulator and demodulator and to open their contacts associated with the normal modulator and demodulator. The emergency carrier voltage is now effective in the emergency modulator and demodulator and ineffective in the normal modulator and demodulator, in so far as any eflect on signals in the respective outgoing and incoming'transmission lines 52 and I4 is concerned.

The foregoing action is substantially identical with the corresponding action of Fig. 3.

Due to the previously pointed out effect between the series-opposing and series-aiding relationship" of the respective windings 04 and 85, and 98 and 91, a voltage from the emergency carrier source 5! of Fig. 4 would cause equal and opposite voltages to be induced in the windings 94 and 86. Consequently, the emergency carrier voltage would cause substantially no emergency carrier current to flow in the normal carrier circuit 61. Hence, relatively high loss would exist from the emergency carrier branch 8 to the normal carrier branch 81.

A voltage applied at either the emergency modulator or demodulator in Fig. 4 would cause approximately equal currents to flow in the resistances is and 84 of the respective normal and lator and demodulator so that substantially no transmission would occur from either of the former to both the latter. Also, a relatively high transmission loss would be provided between the emergency modulator and demodulator and be tween the normal modulator and demodulator for the reasons pointed out with regard to the normal operation of Fig. 4.

at least three wound cores would be required to achieve a corresponding result; in addition, such connection tends to reduce substantially harmonies,- or modulation effect, produced by the wound magnetic coils for the reason that the present invention employs but two wound magnetic cores while other systems known heretoi'ore would embody at least three wound magnetic cores. This means that cheaper magnetic cores and windings from the modulation effect standpoint may be used in the wound magnetic cores without exceeding a certain tolerable modulation effect. Furthermore, a limit of two wound magnetic cores tends to reduce substantially transmission loss occasioned thereby. Consequently, from this loss standpoint cheaper wound magnetic cores may be employed while at the same time maintaining a certain over-ail transmission loss.

Moreover, the maintenance oi impedance matches to obtain eiilcient operation of the necessary filters, although not shown in the drawing, involves relatively severe reflection requirements. A limit of two wound magnetic cores as in Fig. 3 in accordance with the present invention over the requirement of at least three wound magnetic cores in heretofore known arrangements for the same purpose tends to simplify impedance matching and thereby to maintain y In addition, a control of transmission loss in the wound magnetic cores per se is readily accomplished as the previously mentioned relatively high transmission loss between the normal modulator and demodulator depends on the impedance match of the respective normal and emergency carrier branches I1 and 68 to the balancing network l7, in Fig. 3, or the balancing network 38 in Fig. 4, and the high transmission loss between the emergency modulator and demodulator depends on the impedance match of the respective normal and emergency carrier branches 6'! and 68 to the balancing network it in Fig. 3, or the balancing network 36 in Fig. 4. Obviously, such simplification of impedancematching is unable of accomplishment in arrangements heretofore requiring more than three wound magnetic cores. The foregoing advantages apply similarly to Fig. 4 requiring a minimum of four magnetic core coils which minimum is less than other systems of the same general type said tour other circuits, and another or said bu.

ancing networks being applied across the midtion with a carrier transmission system, it is'not neceessarily limited thereto and may be expeditiously adapted to any electrical system tor electromagnetically connecting a plurality of discrete circuits with each other such that diilerent amounts oi. transmission loss exist therebetween;

that suitable signaling circuits maybe substituted for the balancing networks shown in the several figures of the drawing; and that the present invention is to be considered as limited by the scope or the appended claims.

What is claimed is:

i. In combination, a plurality of discrete electrical circuits, and a plurality of multiwinding magnetic core coils to connect electromagnetically said circuits with each other such that relatively low transmission loss exists between each of two circuits and the other circuits, said coils including a pair of magnetic cores and a plurality of pairs of windings connected-to said plurality of circuits and applied to said cores such that one winding of each of two pairs of windings connected to said two circuits and apair of windings connected to two of said other circuits are on one core and the other winding of each of said two pairs of windings connected to said two circuits and a further pair of windings connected to a further two of said other circuits are on a second core.

2. In combination, a plurality of discrete electrical circuits, and a plurality of multiwinding magnetic core coils to connect electromagnetically said circuits with each other such that transmission is effective between each of two circuits and the other circuits, said coils including a plurality of magnetic cores and a plurality of pairs of windings connected to said circuits and applied to said cores such that the pairs of windings connected to said other circuits are on at least two different cores and one winding of each of two pairs of windings connected to said two circuits is individual to one of said two different cores.

3. In combination, a plurality of electrical circuits, a plurality of balancing networks, and means comprising a plurality of multiwinding magnetic core coils to connect electromagnetical- 1y said circuits with each other such that relatively low transmission loss is provided between two circuits and each of four other circuits and relatively high transmission loss is provided between said two circuits and between each of said four other circuits and the remaining circuits thereof, said coils comprising a pair of magnetic cores and a plurality of pairs of windings connected to said circuits and applied to said cores such that one pair of windings in series in a common side of two circuits of said four other circuits and one winding of each of two other pairs of windings connected to said first-men tioned two circuits are on a first core and a further pair of windings in series in a common side of a further two circuits of said four other circuits and the other winding of each of said two other pairs of windings connected to said first-mentioned two circuits are on a second core, said two other pairs of windings having a seriesaiding and series-opposing relationship, one of said balancing networks being applied across the mid-point of said one pair of series windings and another common side of said first two circuits of point of said iurther pair or series windin'gs and another common side of said further two circuits of said four other circuits. I 4. In combination, a' plurality of electrical circuits, a plurality of balancing networks, and

means comprising a plurality of multiwinding magnetic core coils to connect electromagnetical- 1y said circuits with each other such that relatively low attenuation is provided between two circuits and three or more other circuits and relatively high attenuation is provided between said two circuits and between each of said other circuits and the remaining circuits thereof, said coils comprising a plurality of magnetic cores and a plurality of pairs of windings connected in'individual pairs to individualcircuits-and 'applied to said cores such that one winding of each of two pairs of windings connected to said firstmentioned two circuits and two pairs of windings connected to each two circuits of said other circuits are on each pair of two adjacent pairs of said cores, said two pairs of windings connected to said first-mentioned two circuits having a series-aiding and series-opposing relationship and said two pairs of windings connected to 'each two circuits of said other circuits having a seriesaiding and series-opposing relationship, and a winding on one core of each pair. of said adja cent pairs of cores coupling one of said net-' circuit means to connect certain of said circuits with said paths, means comprising a plurality of multiwinding magnetic core coils to connect electromagnetically said circuits with each other such that transmission is etfective between each of two other circuits of said circuits and at least magnetic cores and a plurality of pairs of windings connected to said circuits and applied to said cores such that a first core embodies one pair of windings connected to two of said certain circuits and one winding of each of two other pairs of windings connected to said two other circuits and a second core embodies a further pair of windings connected to two further circuits of said certain circuits and the other winding of each of said two other pairs of windings connected to said-two other circuits, said two pairs of windings applied to both said cores being arranged in a series-aiding and series-opposing relationship, a balancing network applied to the pair of circuits embodying the pair of windings individual to each of said cores, and switching means to render said two other circuits and said certain circuits eifective selectively in said transmission paths.

6. In combination, signal transmitting and receiving paths, normal and emergency signal modulating and demodulating apparatus, normal and emergency carrier wave generators, circuit means to connect said normal and emergency ,modulating and demodulating apparatus to said paths, a pair of balancing networks, switching means to render effective selectively said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier generators in said paths, and means comprising a plurality of multiwinding magnetic core cons interposed between said modulating and demodulating apparatus and said carrier generators to provide electromagnetic connection therebetween such that substantially minimum attenuation is ei'iectively provided be tween either of said carrier generators and said normal and emergency modulating and demodulating apparatus and substantially maximum attenuation is eii'ectively provided between said normal modulating and demodulating apparatus, between said. emergency modulating and demodulating apparatus, between said normal and emergency carrier generators, and between each of said modulating and demodulating apparatus and the other apparatus thereof, said coils comprising a pair of magnetic cores and a plurality of pairs of windings. connected to said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier generators and applied to said cores such that the pair of windings connected to said normal modulator and demodulator is on one core, the pair of windings connected to said emergency modulator and demodulator is on the other core and the pairs of windings connected to said normal and emergency carrier generators are on both saidcores in a seriesaiding and series-opposing relationship, one of said balancing networks is connected across' the mid-point of the pair oi windings on said one core and a portion of said circuit means common to both said normal modulator and demodulator and the other of said balancing networks is connected across the mid-point of the pair of windings on said other core and a portion of said circuit means common to both said emergency modulator and demodulator.

7. In combination, signal transmitting and receiving paths, normal and emergency signal modulating and demodulating apparatus, normal and emergency carrier wave generators, circuit means to connect said normal and emergency modulating and demodulating apparatus nected to said normal modulator and demodulator and a second pair of adjacent cores embodies the other winding 01 each of the pairs of windings connected to said normal and emergency carrier generators and in a series-aiding and series-opposing relationship the pairs of windings connected to said emergency modulator and demodulator, the pairs of windings connected to said normal and emergency carrier generators being arranged in a series-aiding. and series-opposing relationship, a winding on one core of said first adjacent pair of cores coupling one of said balancing networks to said windings connected to said normal modulator and demodulator, and awinding on one core of said second adjacent pair of said cores coupling the other of said balancing networks to said windings connected to said emergency modulator and demodulator.

8. In a signaling system, an outgoing transmission path, an incoming transmission path, normal and emergency modulating and demodulating apparatus, normal and emergency carrier wave generators, circuit means to apply said normal and emergency modulating and demodulating apparatus to said paths, means to connect electromagneticaliy said normal and emergency "modulating and demodulating apparatus with to said paths, a pair of balancing networks,

switching means to render effective selectively said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier generators in said paths, and means comprising a plurality of multiwinding magnetic core coils to connect electromagnetically said normal and emergency modulating and demodulating apparatus to said normal and emergency carrier generators and said networks such that carrier energyirom either of said carrier generators is simultaneously transmitted to said normal and emergency modulating and demodulating apparatus and transmission is eii'ectively prevented between said normal modulating and demodulating apparatus, between said emergency modulating and demodulating apparatus, between said normal and emergency carrier generators, and between each of sair normal and emergency modulating and demodulating apparatus and the remaining apparatus thereof, said coils comprising a plurality of magnetic cores, a plurality oi pairs of windings connected in individual pairs to each of said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier generators and applied to said cores such that a first adja ent pair of said cores embodies one win nl each of th P8 3 01' windings connected to Said normal and emergency carrier Ienerators and in a series-aiding and series-opposing relationshlp the pairs of windings consaid carrier generators, said connecting means comprising'a plurality of pairs of windings, two of which pairs are individually applied across each of said carrier generators and two of which pairs are individually connected in series in one common side of each or said normal and emergency modulating and demodulating apparatus, a pair of balancing networks, one of which networks is applied across a Junction point of one pair of windings in said one common side of said normal modulating and-demodulating apparatus and a junction point of another common side of both said latter apparatus and the other of which networks is applied across a junction point of the other pair of windings in said one common side of said emergency modulating and demodulating apparatus and a junction point of another common side of both said latter apparatus, and a pair of magnetic cores, said windings and said cores arranged such that one core embodies one winding of each oi said pair of windings associated with each of said carrier generators and said pair 01 windings associated with said normal modulating and demodulating apparatus and the other core embodies the other winding of each of said pair of windings associated with each of said carrier generators and said pair of windings associated with said emergency modulating and demodulating apparatus, said individual pairs of windings applied to said carrier generators being arranged on said cores in series-opposing and series-aiding relationship, and switching means to render said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier apparatus effective in desired combinations in both said transmission paths.

9. In a signaling system, an outgoing signaling transmission path, an incoming signaling transmission path, normal and emergency signal modulating and demodulating apparatus, normal and emergency carrier wave generators, a pair of balancing networks, circuit means to apply said normal and emergency modulating and demodulating apparatus to said paths, means to connect electromagneticaliy said normal and emergency modulating and demodulating apparatus with said carrier generators, said connecting means comprising a plurality of pairs of windings two of which pairs are individually applied across each of said carrier generators, four of which pairs are individually applied across each of said normal and emergency modulating and demodu-.

lating apparatus, a single winding to connect one balancing network to said windings connecting said normal modulating and demodulating apparatus, a single winding to connect the other balancing network to said windings connecting said emergency modulating and dembdulating apparatus, a plurality of magnetic cores, said cores and windings arranged such that a first core embodies one winding of each of said pairs applied to said normal modulating and demodulating apparatus and said winding connecting said one balancing network therewith, a second core embodies said other winding of each of said pairs applied to said normal modulating and dcmodulating apparatus and one winding of each of said pairs applied to each of said carrier generators, a third core embodies the other winding of each of said pairs applied to each of said carrier generators and one winding of'each of said pairs applied to said emergency modulating and demodulating apparatus, and a fourth core embodies the other winding of each of said pairs applied to said emergency modulating and demodulating apparatus and said winding connecting the other balancing network therewith, the pairs of windings on associated pairs of cores being arranged in a series-aiding and series-opposing relationship, and switching means to render said normal and emergency modulating and demodulating apparatus and said normal and emergency carrier generators effective selectively in both said paths.

' circuits, each pair of windings being individual to one of said circuits, and applied to said cores such that each winding of the pair of windings connected to said one circuit is on one of two difierent cores and one winding of each of two pairs of windings connected to at least two of said other circuits is on one of said two different cores and the other winding of each of said two pairs of windings connected to said two other circuits is individual to one of two further cores.

11. In combination, a plurality of discrete electrical circuits, and means to connect electromagnetically said circuits with each other such that transmission is effective between each of two circuits and the other circuits, said means including a plurality of magnetic cores and a plurality of windings connected to said circuits, each pair of windings being individual to one of said circuits, and applied to said cores such that one winding'of each of the two pairs of windings connected to said two circuits is on one of two different cores and one winding of each four pairs of windings connected to four of said other circuits is on one of said two different cores and the other winding of each of said four pairs of windings connected to said four other circuits is on one of two further cores.

NELSON BOTSFORD. 

